Foamed urethane, non-elastic crimped fiber battings, resin-bonded or hardened fabric made of non-elastic crimped fibers etc. are currently used as cushioning materials for furniture, beds, trains, automobiles and so on.
A foamed-crosslinked urethane has, on the one hand, superior durability as a cushioning material but has, on the other hand, poor moisture and water permeability and accumulates heat to cause stuffiness. In addition, since it is not thermoplastic, recycling of the material is difficult and waste urethane is generally incinerated. However, incineration of urethane gives great damage to incinerator as well as necessitates removal of toxic gases, thus causing great expenses. For these reasons, waste urethane is often buried in the ground. This also poses different problems in that stabilization of the ground is difficult, with the result that burying site is limited to specific places as necessary costs rise. Moreover, although urethane exhibits excellent processability, chemicals used for its production reveal a possibility of causing environmental pollution.
When a thermoplastic polyester fiber batting is used, the problems of inpersistent shape, degraded bulkiness and degraded resilience due to fiber movement and fatigue of crimps as a result of unfixed, loose relations of the fibers are caused. Incidentally, Japanese Patent Unexamined Publication Nos. 11352/1985, 141388/1986 and 141391/1986 disclose fabric of polyester fibers bonded by an adhesive such as a rubber-based adhesive. Also, Japanese Patent Unexamined Publication No. 137732/1986 discloses one using crosslinked urethane. These cushioning materials are inferior in durability and pose problems of unattainable recycling since it is not thermoplastic nor of a single composition, complicated steps for processing, pollution by the chemicals used for the production and so on. A polyester hardened fabric, such as those disclosed in Japanese Patent Unexamined Publication Nos. 31150/1983 and 220354/1991, and U.S. Pat. No. 5,141,805 is inferior in durability as demonstrated by deformed shape and lowered resilience thereof caused by the use of a brittle amorphous polymer as the bonding component for heat-bonding fibers (e.g. those disclosed in Japanese Patent Unexamined Publication Nos. 136828/1983, 249213/1991) to allow easy breakage of the bonded portions during use. As a method for overcoming the defect, Japanese Patent Unexamined Publication No. 245965/1992 proposes an interlocking treatment. Yet, the brittleness of the bonded portions which brings about marked decrease in resilience cannot be overcome by the proposed treatment. Such polyester fabric encounters with difficulties in processing thereof and in providing a soft cushioning material due to the resistance to the deforming of the bonded portions. In view of these problems, there have been proposed a heat-bonding fiber using a polyester elastomer having soft and deformation-recoverable bonded portions (Japanese Patent Unexamined Publication 240219/1992) and a cushioning material using said fiber WO-91/19032). The adhesive polyester elastomer used for this fiber structure comprises terephthalic acid in a proportion of 50-80% by mole as an acid component for a hard segment and polyalkylene glycol in a proportion of 30-50% by mole for a soft segment and isophthalic acid and so on as another acid component as in the fiber disclosed in Japanese Patent Publication No. 1404/1985 so as to increase noncrystallinity, which will result in a lowered melting point thereof to not more than 180.degree. C. and a low melt viscosity to contribute to an improved amoeboid shape heat-bonding. Still, the fiber is susceptible to plastic deformation which causes poor heat resistance and poor resistance to compression.
Japanese Patent Unexamined Publication No. 44839/1972 discloses a thermoplastic olefin net structure suitable for use in construction works. Different from cushioning structures made of thin fibers, the surface thereof is not smooth but rough and heat-resisting durability is markedly poor due to the use of olefin as a base material, to the point it is not usable as a cushioning material. While there have been proposed net structures made from vinyl chloride for use for entrance mat etc., they are not suitable as cushioning materials in view of the fact that plastic deformation easily occurs and toxic hydrogen halide is generated upon incineration.
Accordingly, an object of the present invention is to solve the aforementioned problems and to provide a cushioning net structure which can be prossessed into unstuffy cushions having superior heat resistance, durability and cushioning function, and which can be recycled easily, and a method for the production thereof.